Apparatus for determining the bursting strength of sheet material



Feb. 1, 1944. r J. DA.. CLARK APPARATUS FOR DETERMINING THE BURSTING STRENGTH OF SHEET IV IATERIAL Filed April 2 2 Sheets-Sheet 1 Feb. 1,1944. J, M CLAR 2,340,791.

APPARATUS FOR DETERMINING THEBURSTING STRENGTH OF SHEET MATERIAL Filed April 2, 1942 2 Sheets-Sheet 2 44 ,5 69AM, M awm ,0 77 I6 Q I I V l 75 f3 1a 5 V f w dag,

Patented Feb. 1, 1944 f t i APPARATUS FOR DETERMINING THE nuas'rmc sraENG'rnor snnn'r MATE- James dA. Clark, Appleton, Wis assignor to The Institute of Paper Chemistry, a corporation of Wisconsin Application April 2, 1942'. Serial st. 431,354

- comma. (crass-1'4) The present invention is'directed-to improvements in apparatus for testing the b strength of paper and like material.

One of'the specifications on. which sold is its so-called "bursting strength." In determining this property, samples from 'a lot of paper are placed in suitable testing apparatus,

such as the Mullen or Schopper-Dalen machine,

. one at a time, and the pressure which a certain area of each. sample will withstand before bursting is measured. Because of theimportanc'e of these tests as a measure of the strength or paper, very serious efforts have been made by TAPPI and like organizations to develop standard test-I ing procedures and apparatus which will. give 'truly comparative and readily reproducible results. Some progress has been made, but with the apparatus and procedures at present avail-- able, the results obtained are subject to considerable variation and are generally incapable of reproduction on different machines, or sometimes even on the same machine with different operators. It appears that some of these difllculties result either from inherent characteristics of the particular apparatus used or from the condition of theapparatus at the time of the test. In addition procedural differences, even if slight,

resulting from operation of the machine by different operators aresuflicient .to affect the precision of the results obtained materially. In brief, bursting strength tests on known apparatus p per is apparatus shown in Fig. 1;

Fig.1 is a top plan view of apparatus embodying the present invention for testing the bursting strength of paper; e Y Fig. 2 isa front elevational view of the testing Fig.3 is avertical sectional view taken gen- L -orally on line 3-4.0: Fig. 1, certain parts being a broken. away, and showing the initial positions -oi' the movable parts of the testing apparatus and, by known procedures are not only lacking in precision, but in addition are incapable of reproduction.

As a result, there is a great need in the paper making industry for an improved testing apparatus and procedure for use in determining the brusting strength of paper, and particularly is therea need for a testing apparatus and procedure which will give more precise and more readily reproducible results than the available apparatus and procedures. The supplying of this the neutral position:

Fig. 5 is a view similar to Fig. 4 illustrating the manner in which the paper sample is finally burst when ,testedjfor bursting strength in the 1 apparatus? Fig. 6 is an enlarged fragmentary view showing certain of the details of the sample holding means constituting a part of the apparatus:

- Fig. "I is a vertical sectional view taken on line 8- 6 of'Fig. 1 through a tour-way control valve -i or the testing apparatus of Figs. 1 and 2 with the operating member of the valve being in Fig. 8 is a sectional view through the valve similar to Fig. '7, but with the valve operating memberadvanced to the position whereby the testing apparatus'is operated to the clamping'position shown in Fig. 4;

Fig. 9 is a vertical sectional view control valve similar to Fig. 7, but showing the valve operating member in a still further .ad-

vanced position so as to operate the tester to the stage of operation illustrated in Fig. 5; and

Fig. 10 is a vertical sectional'view through the control valve similar to Fig. 7, and showing the operating member 01 the valve in its final position whereby the parts oi testing apparatus are permitted to resume their initial positions shown in Fig. 3. 1

need is the primary object of the present invention. As will hereinafter appear, this object is accomplished by the provision of bursting strength testing apparatus which is substantial-,

1y completely automatic in operation, being controlled by the operation of a single valve, and

by the provision of other novel features which will be described.

For a more complete understanding of the nature and scope of my invention, reference may be had to the following detailed description thereof taken in connection with the accompanying drawings in which:

Referring particularly to the first three figures or the drawings, the testing apparatus of my invention is indicated generally at 5 and comprises a rigid, cast metal, main frame 8 on which the various parts of the apparatus are mounted., The base 8 of the frame is generally rectangular in outline, about 3 inches wide, 5 inches high, and 9 inches long. Rubber feet '7 or the like are provided on the underside of the base portion 8 so that the apparatus may be conveniently supported on a table or bench. The left hand portion of the frame 6 includes an open, rigid,

yoke '9 having a flat, horizontal portion In when ready tohave a paper sample tested there- Fig. 4 is a view similar to Fig. 3 showing the positions oftheparts of the testing apparatus when the sample oipaper is clamped therein;

control through the which serves as a platen for holding the sample being tested. The right hand portion of the apparatus includes a pressure gauge II and a control valve l2. Suitable piping interconnects the different pafts of the apparatus as will appear hereinafter. 1

The platen portion IU of the frame 6 is provided with a circular recess l3 formed in the face thereof, and a circular rubber gasket I4 is placed in this recess. A disc member I 5 having the form of a truncated cone overlies the gasket l4. The disc I5 is of less diameter than the recess l3, and is held centrally thereof by means of, a small spool l6 which extends through the central portion of the disc l5 and the underlying gasket l4 into a suitable counterbored passageway IT.

A flexible rubber diaphragm 8 which is circular in outline overlies the disc l5. This diaphragm is preferably of thin, pure rubber sheeting, not over about .005 inches thick, dental dam"v rubber sheeting being particularly satisfactory for the purpose. The flexible diaphragm 18 is of substantially the same diameter as the recess l3, and hence extends beyond the lower diameter of the disc I5, as shown. The diaphragm I8 is held in place during the operation of the machine by an annular clamping or sealing ring l9 which is disposed thereon.

The underside of the inner circular edge of the clamping ring is is beveled at an angle corresponding to the angle of the truncated edge portion of the centrally located .disc member IS. The thickness of the clamping ring I9 is such that the upper surface thereof is substantially in the same plane as the upper surface of the rubber diaphragm l8 when the assembly is placed under pressure during the operation of the apparatus. The clearance between the opposed beveled surfaces of the disc l5 and the clamping ring I! should be sufllcient to leave the diaphragm l8 free in this conical area. This prevents marking of the sample during the clamping operation. The outer edge of the under surface of the clamping ring I9 is undercut as shown at 20 in Fig. 6 to aid in securing a tight clamping pressure on the outer edge of the diaphragm l8.

The section of the main frame 6 directly above the platen portion l2 servesas the housing for the operating parts of theautomatically operated sample holding means. The upper part of this housing comprises a short cylinder 2| in which there is disposed a relatively thin, large diameter, loosely fitting piston 22. The upper end of the cylinder 2| is closed by a cylinder head 23 secured thereto by a number of spaced cap screws 24, as shown. A flexible, rubber diaphragm 26 of heavier material than the diaphragm I8 is secured between the cylinder 2| and the cylinder head 23. During the operation of the apparatus pressure air is admitted to the upper side of the diaphragm Is to force down the piston 22. The diaphragm 26 fits just inside of the row of cap screws 24.

A cylindrical clamping head 30 which cooperates with the platen assembly to hold the sample being'tested during the operation of the'apparatus is carried on the underside of the piston 22 by an integral interconnecting shank 3|. In order toguide the clamping head 30 into proper engagement with platen assembly, the cylinder 2| includes a cylindrical skirt or guide portion 32 which loosely engages the sides of the head 30. An annular shoulder 29 is provided in the lower end of the guide portion 32 for retaining the lower end of a compression spring 34, as shown.

The compression spring 34 is compressed between the shoulder 29 and the underside of the piston 22 so as to normally force or bias the piston 22 upwards against the closed end of the cylinder 2|.

6 The clamping head 30 is thereby held in its upper retracted position as shown, in Fig. 3.

The face of the' clamping head 30 is annular in outline and is provided with a central recess 35 into which the rubber diaphragm i8 is adapted to burst each paper sample, as will appear hereinafter. The clamping head 3|] is provided with a vent 36, and the skirt or guide portion 32 is provided with a cooperating vent 31 designed to obviate the building up of pressures within the i6 cylinder 2|. It will be seen that by virtue of the construction of the parts above mentioned the clamping head 30 is free to float axially to a limited extent, if necessary. so as to secure perfect alignment of the face of the clamping head '30 and the face of the clamping or sealing ring l9 when a sample of paper is placed therebetween.

The apparatus is adapted to be completely controlled by the operation of the single valve l2 which is located on the right-hand side of the frame 8, as shown in Figs. 1 and 2. The valve l2 consists of a stationary outer part 4|. and a movable, inner operating member 42 (Fig. 7), and is of the four-way type, the outer valve part 4| being provided with four ports 43, 44, 45 and 46 leading into the interior of the valve. As shown in Fig. 7, the valve ports 43, 44, 45 and 46 are each spaced about 45 angular degrees apart, although it will be understood that this particular arrangement is not essential. The operating member 42 is provided with an arcuate groove 41 in the side'thereof for. the purpose of interconnecting the valve ports 43, 44, and 46 in a plurality 'of different combinations as will be ex- I plained hereinafter in connection with Figs. 7

4 through 10 of the drawings.

The valve body 4| is drilled out in three places so as to provide for the connection of pipes with the three valve ports 43, 44 and 45. The fourth valve port 46 opens directly to the atmosphere and no pipe connection is made thereto. A pipe line 50 connects the valve port opening 43 with a source of fluid pressure, preferably compressed air. A plug fitting 5| screwed into the underside of the valve l2 connects a pipe line 52 into the valve port 44. The other end of the line 52 (Fig.

2) is connectedby a similar plug fitting 53 into a pressure inlet 54 integrally formed on the side of the cylinder head 23. The cylinder head 23 is 65 provided with small passageways 55a and 55b 54'to the top of the rubber diaphragm 26.

The inlet side of a needle valve 55 is threaded into the left hand side of the control valve I2 so as tocommunicate with the valve port 45. The needle valve 56 is provided with the usual adjusting screw 59 and has two outlet connections 51 and 58. The outlet opening 58 is interconnected in pressure conductive relationship with the underside of the sample bursting diaphragm is by a conduit or line 60, one end of which is connected into the outlet 58, and a plug fitting 8|. The frame 6 is provided with a small passageway 62 (Fig. 3) which connects the inlet fitting 6| through the passageway I1 and the spool It to the underside of the sample bursting diaphragm i8.

The other outlet 5? of the needle valve 56 is connected to the pressure gauge H by a pipe line 58 as shown in Fig. 2. The same fluid pressure will be transmitted from the control valve It 25 through the needle valve 56 to each of the outlets (Figs. 2 and 3) which connect the pressure inlet 1 ple bursting diaphragm l8 'll. As shown in Fig. 1,

s eaves that conducted .The operation of the apparatus in determinin the bursting strength of paper samples is as follows: At the beginning of operating handle 12 which is mechanically connected to the operating member 42 should be in a substantially vertical position. die in this position the valve operating member 42 will bein the position shown in Fig. 7, the valve port 53 through which compressed air is applied to the valve l2 communicating only with the arcuate groove ill. The movable parts of the apparatus will be in their initial positions'shown in Fig. 3, the compression spring 34 holding the piston 22 against the cylinder head 23 so that the clamping head 30 is in its elevated or retracted position over the platen l2. A sample piece of paper 15 to be tested is now placed on the top of each test the valve With the hanthe sample bursting diaphragm l8 forming a part of the platen assembly as shown in Fig. 3.

Next the valve handle 12 is turned about 45 in a clockwise direction so that the valve operating memberdZ will be turned to the position shown in Fig. 8. This moves the arcuate groove ti to effect interconnection of the valve ports 53 and dd. Thereupon pressure will-be transmitted from the the valve W and the line I 52 to the top of the rubber diaphra it. The

supply line 50 through fluid pressure acting on the top of the diaphragm 2t expands that member as to force the piston 22 and clamping head downwardly as shown in Fig. 4. By this movement of the piston 22 against the resistance of the spring 85, the clamp ing head 39 is forced against the diaphragm clamping ring l9 and the other parts of the platen assembly so as to hold the paper'sample idand the sample bursting diaphragm is therebetween. The force applied to the clamping head should be sumcient so that the diaphragm i8 is held in fluid tight relationship against the bed of the platen lil.

The next movement in the operation of the apparatus is to turn the operating handle 12 about further in a clockwise direction so as to bring the valve operating member d? to the position shown in Fig. 9. In this position the arcuate groove 41 interconnects the three valve ports 53, dd, and t5. Fluid pressure continues to be transmitted to the upper side of the rubber diaphragm 26 in the clamping head 38 in the sample holding position with a fixed, predetermined pressure. At the same time fluid pressure is also transmitted through the valve port 65 into the inlet side of the needle valve 56. From the needle valve 56 the pressure will be transmitted through the line So to the underside of the sample bursting diaphragm it. As a result, the diaphragm is will be caused to expand into clamping head 3t against the restraint of the paper sample 15 which is clamped between the clamping head 39 and the platen assembly. The needle valve 5% is adjusted so that the pressure is supplied gradually to the underside of the diaphragm It so as to be closely followed by the needles 7!! and ll of the pressure gauge ll. Finally, the pressure under the rubber diaphragm it will reach a value where the paper sample '35 the recess 35 in the cylinder 2| so as to hold the is burstlnto the recess 35 as 'Ihereupon the pressurebeneath the diaphragm l8 momentarily drops because'the. rubber diaphragm It will now further expand. The diaphragm I8 is restrained from bursting *bythe walls of the recess 35. The'maxirnum pressure attained will be indicated on the pressure gauge panded diaphragm It builds up to that previously required to burst the p p r, or the gauge will register an erroneous maximum. With a normal setting of needle valve 56, adequate time is avail-' able for this motion. In the Fig. 10 positiomthe three valve ports, dB and 46 areinterconnected and the-compressed. air port 43, is disconnected .from those three ports. Accordingly, the pressure in the upper side of the diaphragm 25 will be released and the compression spring 36 will retract the piston 22 and diaphragm 26' upwardly .against the cylinder head 23, as shown inFig. 3.

The pressure air is releasedfro'm the cylinder 2| through the line 52 and out'through the dis-- charge port do. With the clamping head all withdrawn, most of the pressure underneath the rubber diaphragm is is released .by leakage directly from the underside thereof around the edges of the circular recess in the platen [0. As explained above, the diaphragm clamping rlngflw fits fairly loosely in the platen l2 and thereby permits free release of the pressure under the sample bursting diaphragm it when the clamping head so is raised. A small portion of thefluld pressure under the diaphragm is may leak back through the line ti! and needle valve 56 and out through the valve port $6. l

The valve 52 may b provided with a fifth port through which pressure can be supplied for retracting the piston 22 during thecycle of operation. The piston may also be inverted sothat its own weight will serve to retract it.

The reading indicated by the handlll is recorded as the bursting strength of the sample 15 and the,hand it is thenreset to zero position. The burst paper sampl i5 is removed from the apparatu and anothersample is inserted in place on the platen assembly and diaphragm is and the above operations are repeated. It will beseen that the valve control handle 12 may be tumed in a clockwise direction directly from the position thereof corresponding to Fig. 10 .to the position corresponding to Fig. 8 without stopping at the intermediate position corresponding to Fig. '7.

From the foregoing description, it will be seen that paper samples may be tested for their bursting strength in the apparatus solely by the operation of the valve ii. The operation of the appa-' ratus is substantially completely automatic and this results in considerable saving of time, as

compared with prior procedures. Furthermore,

the rate of loading on the underside of the paper sample 15 may be readily controlled to that desired or as specified for any testing procedure by adjusting the opening in the needle valve 55. By

' using air as an operating medium a substantially uniform rate of increase of bursting pressure is obtained in contrast to. liquid operated testers commonly in use wherein a uniform volume of liquid per second is pumped to the underside of 3f indicated'ln Fig. 5.

the sample bursting diaphragm l8. In such liquid operated testers the rate of loading is low at the beginning. then rapidly, accelerates until when. the specimen is burst the rate is usually so great that the inertia of the moving parts in the maximum hand pressure gauge ll carries the indicating needle an uncertain and uncontrollable substantially beneath that of the plane of the specimen, no diaphragm error is introduced in the reading. Diaphragm error is present in certain of such prior apparatus because of the uncertain pressure required to extend the sample bursting diaphragm so as to contact the underside of the specimen uniformly and before a stress is applied to the specimen.

' Since it is obvious that the principles of my invention may be embodied into different modiflcations of paper testers, it is lntended'that all matter described above or shown in the accompanying drawings shall be interpreted aslllustrative and not in a limiting sense.

I claim:

1. In apparatus for determining the bursting strength of sheet materials, in combination, a rigid platen means for supporting a sheet of the material to be tested, said platen means having a flat upper surface and a recess formed in said surface, an extensible diaphragm, means including a flat disc and an annular clamping ring for supporting said diaphragm within said recess, the relative dimensions of said recess and said diaphragm supporting means being such that said diaphragm is normally disposed substantially coplanar with the flat surface of said platen means, a clamping head movable into and out of engagement with said platen means, means including a piston for moving said clamping head into engagement with said platen means with predetermined pressure so as to hold the material being tested in surface contact with said diaphragm, a recess in the face of said clamping head into which the material being tested and said diaphragm may be forced during test, a source of fluid pressure, meangs including piping and a control valve having four positions for connecting said source of fluid pressure to said piston and to said diaphragm for effecting the operation of said apparatus, said means being operable when said valve is in the first position to cause said clamping head to be held out of engagement with said platen, being operable when said valve is in the second position to move said piston and clamping head into engagement with said platen and said diaphragm support means, being operable when said valve is in the third position to apply pressure to the side of said diaphragm which is. opposite said clampinghead to accomplish the bursting of the material being tested, and operable when said valve is inthe fourth position to disconnect said source of fluid pressure and relieve the pressure previously applied to said piston and diaphragm,

and means for indicating the pressure which is applied to said diaphragm during the operation of said apparatus.

2. In apparatus for determining the bursting strength of sheet materials, incombinatlon, a rigid platen means for supporting a sheet of the material to be tested, said platen means having a flat upper surface and a recess formed in said surface, an extensible diaphragm, means includ-' ing a flat disc and an annular clamping ring having opposed cooperating surfaces for engaging said diaphragm and for supporting said diaphragm within said recess, the relative dimensions of said recess and said diaphragm supporting means being such that said diaphragm is normally disposed substantially coplanar with the surface of said platen means, a clamping head movable into and out of engagement with said platen means, a spring normally biasing saidclamping head out of engagement with said platen means, means including a piston for moving said clamping head into engagement with said platen means with predetermined pressure so as to hold the material being tested in surface contact with said diaphragm, a recess in the face of said clamping head into which the material being tested and said diaphragm may be forced during test, a source of fluid pressure, means including piping and a control valve having four' positions for connecting said source of fluid pressure to said piston and to said diaphragm for effecting the operation of said apparatus, said means being operable when'said valve is in the first position to disconnect said source of fluid pressure from said apparatus, being operable when saidvalve is in the second position to admit. fluid pressure to said piston and thereby to cause said piston to move said clamping head into engagement with said platen and said diaphragm support means against the force oi said biasing spring, being operable when said valve is in the third position to apply pressure at a predetermined, controllable, uniform rate to the side of said diaphragm which is opposit said clamping head to accomplish the bursting of the material being tested, and operable when said valve is in the fourth position to disconnect said source of fluid pressure from said apparatus and to relieve the pressure previously applied to said piston and diaphragm, and means for indicating and recording the pressure which is applied to said dia- JAMES nA. CLARK. 

